| Steam-assisted gravity drainage(SAGD)is a mining technology used to increase the recovery rate of heavy crude oil.The principle of SAGD is that steam is injected from the upper part of the oil well,and the heated heavy oil with the decreasing viscosity has a good flowability.Under the effect of gravity,heavy oil flows into the lower part of the oil well and then is pumped out.However,with the large-scale application of SAGD technology in Xinjiang Oilfield,problems such as difficulty in transporting and handling produced liquid in the cyclic preheating stage have become increasingly prominent,and the phenomenon of produced liquid carrying gas and oil-water emulsification has a serious negative impact on the downstream gathering and treatment system.In view of the above problems,this paper focuses on the optimization of transportation and dehydration process,thermal utilization and the development of accompanying equipment.Through the initial testing research,it is found that the use of composite-type coagulant and coagulation-settlement separation process can effectively remove the floating oil and suspended matter from the SAGD cyclic preheating produced liquid.The two-point dosing method can effectively reduce the difficulty of floating oil treatment and decrease the settling time,which can increase the dehydration effect by about 50%.The combination protocol of advanced treatment of produced water with multiple-effect evaporation(MED)and steam power generation proposed by our research group can both shorten system energy consumption and improve comprehensive utilization efficiency of heat energy.In light of the deficiencies in the traditional gathering and transportation technology,an optimization study on the process for gathering and transporting SAGD cycle preheating produced fluid is conducted in this paper.The results show that the new metering process,named “separation-liquid phase cooling-vapor phase condensation metering”,can improve the metering accuracy of produced liquid from SAGD single well,and accurately measure the entrained steam capacity and gas-liquid ratio in produced liquid.In order to meet the design requirements,the horizontal spiral-plate heat exchanger is selected as the heat exchange equipment,DYB(D)series high-temperature centrifugal fuel delivery pump is used as hightemperature pump,and on-line desanding process is adopted for sand-discharge equipment.According to the SAGD circulating fluid treatment process test,each treatment unit under the initial working condition can reach the treatment index required by the design.When the oil content of produced liquid is about 10000mg/L,the dosage of purifying agent and coagulant aid should be 300～400mg/L and 150～250mg/L respectively in order to ensure that the oil cut in the water from the oil-removal settlement tank is less than 4000mg/L and the water cut in the oil is less than 40%.The process optimization and experimental research in this paper provide guiding suggestions for improving the gathering and transportation effect of heavy oil produced fluids and developing efficient treatment processes in Xinjiang Oilfield,which also can provide important reference value for heavy oil production in other domestic oilfields. |
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